Background: Inselbergs are known to influence vegetation patterns worldwide. In extra-tropical areas, opposing slopes of inselbergs have different exposures to solar radiation; for example, in southern South America, north-facing slopes are more exposed to solar radiation than south-facing slopes, both in terms of angle and period of incidence. Aims: We aim to verify whether species diversity and composition and trait convergence and divergence in woody plant communities are associated with differences in the relative solar radiation intercepted by opposing slopes of inselbergs. Methods: We estimated the relative solar radiation intercepted by opposing slopes of seven inselbergs in southern Brazilian Pampa, applying hill shading estimation (HSE) to a digital elevation model. We recorded woody individuals with a diameter at breast height ≥5 cm in 13 plots placed on north-and south-facing slopes. We tested for the association of species diversity and composition and trait convergence and divergence with HSE. Results: Variation in species diversity and composition was associated with HSE. Less exposed slopes were taxonomically more diverse than more exposed slopes. Convergence and divergence of leaf traits were associated with slope exposure. Conclusions: The low-diversity communities on more exposed slopes likely resulted from filtering by environmental variables associated with slope exposure. The higher diversity of tree communities on less exposed slopes might be attributed to diversification of strategies for resource capture and capacity of supporting more niches due to potentially higher water availability. These findings advanced our understanding of the role of slope exposure for plant community assembly in the extra-tropical South America.